Certain electric heat treating vacuum furnaces utilize heating elements, formed of bands or strips of molybdenum, as a source of radiant heat. These elements are typically supported by insulated hangers or standoffs, and may be arrayed in a substantially circular arrangement in the hot zone of the furnace, or in straight sections arranged transversely across the hot zone at the ends thereof. The molybdenum heating elements are connected in either a parallel or series circuit configuration to the electrical power terminals which penetrate the vacuum vessel.
As electrical current is introduced into, and subsequently removed from, the heating elements, they become heated to high temperatures and cooled from those temperatures, respectively. This heating and cooling of the element subjects it to high stresses from expansion and contraction. Such thermal cycling accelerates warping, bending, cracking, and overall distortion of the molybdenum heating elements and reduces their useful life. Furthermore, the potential for damage to the hot zone and contamination of the load in the furnace is increased if a heating element fails catastrophically.
In view of the foregoing problems, it would be highly advantageous to have a means of reducing the adverse effects of the stress on the heating elements that result from thermal cycling.